Therapeutic targeting of CD38 enhances temozolomide activity in glioblastoma cells and modulates their tumor microenvironment by eliciting an enhanced CD8+ T cell response

Abstract

Abstract Glioblastoma (GBM) is an aggressive primary malignant brain tumor with poor prognosis. Surgical resection followed by chemoradiotherapy (temozolomide [TMZ] + radiation) results in a median survival of only 12-15 months. Recently, immunotherapy with targeted antibodies, therapeutic vaccination and adoptive cell therapy offers a promising option for treating GBM. Herein we observed that CD38, a catalytic receptor and regulator of NAD homeostasis, is expressed on GBM cells and their microenvironment in primary patient-derived GBM tissues. Blacher et al have shown that blocking CD38 enzymatic functions results in reduced GBM cell growth. This evidence prompted us to investigate the antitumor and immune engaging effects of a clinical grade anti CD38 therapeutic monoclonal antibody (Daratumumab/DARA) in preclinical models of GBM. We demonstrated that DARA significantly enhanced the direct apoptotic effect of TMZ and induced ADCC/CDC of GBM cells, irrespective of the presence of microglia. In an in vitro 3D simulated GBM + T cell coculture system, DARA induced activation (CD69/GITR upregulation/decreased PD1) and enhanced proliferation of CD8+ T cells/cTL activity against GBM cells. DARA also resulted in increased IFNγ and decreased IL-10; suggesting an improved antitumor cytokine milieu and ensued in downregulated inflammatory cytokine associated JAK2/STAT3 signaling pathway. Finally, we tested TMZ+DARA in a human GBM xenograft in vivo model and noted significantly prolonged survival of mice [TMZ+DARA vs. vehicle: 98.13±1.88 vs. 63.63±3.77 days, p<0.001]. Altogether, these observations led us to investigate the clinical activity of DARA+ TMZ in GBM patients in a phase I/II clinical trial.